In recent years, a semiconductor laser apparatus enabling several watts to one hundred watts is developed. Such a semiconductor laser apparatus is also used as a laser trimmer, laser soldering iron, and a laser marker.
Since the electro-optical conversion efficiency of the semiconductor laser apparatus is approximately 50%, half of power to be introduced can be transferred to heat. Because of this heat, the laser output, efficiency, and life of the element is greatly affected. In order to cool efficiently such heat, a heat sink employing water having high heat conductivity and large heat capacity as a refrigerant is used. For such a heat sink, for example, the following one is known: a fine flow path is formed by combining a plurality of plate-shaped members made of copper, and cooling water is circulated in the flow path. The cooling water cools the semiconductor laser array by carrying out heat exchange with the semiconductor laser array mounted on the upper portion of the flow path (for example, see Patent References 1 and 2).
The aforementioned semiconductor laser apparatus has a stack structure in which a plurality of semiconductor laser arrays are stacked. When a high power output is intended, a plurality of heat sinks each are inserted between the stacked semiconductor laser arrays. These heat sinks not only carry out cooing to the semiconductor laser array, but also fills the role of an electrically conductive path; thus, an electric field is also applied to the heat sink in operation of each semiconductor laser array (for example, see FIG. 1 of Patent Reference 1).    Patent Reference 1: International Publication No. 00/117117 Pamphlet    Patent Reference 2: JP-A-10-209531